**Background:** Heavy metal contamination of food crops is a global concern due to the non-biodegradable nature of toxic metals and their accumulation along the food chain. Tomatoes (Solanum lycopersicum L.) are the most widely planted vegetable globally and a dietary staple in Egypt, where they are cultivated year-round. In Egypt, approximately 6.8 million metric tonnes of tomatoes were produced in 2019. The use of untreated industrial wastewater for irrigation introduces toxic metals (Cd, Cu, Pb, Cr, Zn, Ni, As, Co, Hg) into agricultural soils, which can be taken up by crops and pose health risks to consumers. This study aimed to assess the effects of toxic metals on tomato growth and the potential health consequences for both domestic and international consumers.
**Methods:** The study was conducted in south Greater Cairo, Egypt, during the summer of 2021. Six farms (2 acres each) were selected: three control farms in Abu Ragwan receiving irrigation water from Nile River tributaries, and three contaminated farms in El-Shobak El-Sharky receiving untreated industrial wastewater. Soil samples (0–50 cm depth), water samples, and tomato plant samples were collected. Soil and water were analyzed for pH, electrical conductivity (EC), nutrients (N, P, K), and heavy metals (Pb, Cd, Cr, Cu, Ni, Fe, Mn, Zn, Co) using atomic absorption spectrophotometry. Plant growth parameters (stem and root length, number of leaves, fresh and dry biomass, productivity) were measured. Photosynthetic pigments (chlorophyll a, b, and carotenoids) were determined spectrophotometrically. Bioaccumulation factor (BF = C_root/C_soil) and translocation factor (TF = C_shoot/C_root) were calculated. Health risk was assessed using daily intake rate (DIR) and hazard quotient (HQ) for adults (body weight 60 kg, daily tomato intake 0.345 kg) and children (body weight 32.7 kg, daily tomato intake 0.232 kg). Statistical analysis used paired-sample t-tests and one-way ANOVA (SPSS v23).
**Key Results:** Irrigation with untreated wastewater significantly altered soil characteristics. Contaminated soil had a slightly neutral pH (6.80 vs. 8.25 in control), higher EC (6.45 vs. 1.98 µs cm⁻¹), and substantially elevated heavy metal concentrations. The pollution load index (PLI) was highest for Pb (183.3), followed by Zn (39.0) and Cr (30.4). Wastewater had high BOD (673.33 mg L⁻¹) and COD (1848.00 mg L⁻¹) compared to control (2.81 and 5.44 mg L⁻¹, respectively). All growth parameters significantly decreased under wastewater irrigation: stem length reduced by 51.4%, root length by 46.3%, number of leaves by 51.6%, leaves fresh weight by 57%, stem fresh weight by 55.2%, fresh biomass by 55.2%, and productivity by 65.9%. Photosynthetic pigments declined significantly: chlorophyll a by 43.5%, chlorophyll b by 55.2%, and carotenoids by 17.9% (non-significant). Heavy metal concentrations in edible fruits were markedly elevated: Fe reached 5000.11 mg kg⁻¹ (98.9% difference from control), Pb 360.67 mg kg⁻¹ (93.8%), Mn 356.33 mg kg⁻¹ (93.7%), and Zn 59.67 mg kg⁻¹ (91.3%). Bioaccumulation factors were >1 for all metals except Cu, with Cd showing the highest BF (815.97), followed by Fe (165.26) and Pb (70.64). Translocation factors >1 were observed only for Pb (TF=1.08) and Ni (TF=1.27). The hazard quotient for contaminated tomatoes exceeded safe thresholds (HQ>1) for multiple metals: Pb HQ was 2073.8 for adults and 2558.9 for children; Cd HQ was 574.0 and 708.3; Fe HQ was 41.1 and 50.7; Mn HQ was 146.4 and 180.6; Zn HQ was 1.1 and 1.4 for adults and children, respectively.
**Clinical Implications:** The consumption of tomatoes grown with untreated industrial wastewater irrigation poses a severe health risk due to toxic metal accumulation. The hazard quotient values for Pb, Cd, Fe, Mn, and Zn far exceed the threshold of 1, indicating a high risk of long-term adverse health effects. Lead exposure is particularly concerning given its neurotoxicity, especially in children. The study demonstrates that while tomato plants accumulate most heavy metals in roots (acting as a partial barrier), significant quantities still reach the edible fruits. The authors strongly recommend against cultivating tomatoes as a cash crop in soils irrigated with untreated wastewater due to the unacceptable health risks to consumers. These findings have implications for agricultural policy, wastewater treatment infrastructure, and food safety monitoring in regions where untreated wastewater is used for irrigation.